Tradeoffs: Clojure tags could not override Java/record constructors - not sure that's something we'd ever want to do, but this would cut that off. This alternative may attempt classloading when it would not have before.

Rich Hickey
added a comment - 29/Nov/12 9:36 AM The problem assessment is ok, but the resolution approach may not be. What happens should be based not upon what is in data-readers but whether or not the name names a class.
Is the intent here to allow readers to circumvent records? I'm not in favor of that.

New patch following Rich's comments. The decision to read a record is now based on the symbol containing periods and not having a namespace. Otherwise, it is considered a data reader tag. User
defined tags are required to be qualified but they may now have periods in the name. Tests added to show that
data readers cannot override record classes. Note: Clojure-defined data reader tags may be unqualified, but they should not contain periods in order to avoid confusion with record classes.

Steve Miner
added a comment - 29/Nov/12 4:01 PM New patch following Rich's comments. The decision to read a record is now based on the symbol containing periods and not having a namespace. Otherwise, it is considered a data reader tag. User
defined tags are required to be qualified but they may now have periods in the name. Tests added to show that
data readers cannot override record classes. Note: Clojure-defined data reader tags may be unqualified, but they should not contain periods in order to avoid confusion with record classes.

I deleted my old patch and some comments referring to it to avoid confusion.

In Clojure 1.5 beta 1, # followed by a qualified symbol with a period in the name is considered a record and causes an exception for the missing record class. With the patch, only non-qualified symbols containing periods are considered records. That allows user-defined qualified symbols with periods in their names to be used as data reader tags.

Steve Miner
added a comment - 29/Nov/12 4:17 PM - edited I deleted my old patch and some comments referring to it to avoid confusion.
In Clojure 1.5 beta 1, # followed by a qualified symbol with a period in the name is considered a record and causes an exception for the missing record class. With the patch, only non-qualified symbols containing periods are considered records. That allows user-defined qualified symbols with periods in their names to be used as data reader tags.

clj-1100-periods-in-data-reader-tags-patch-v2.txt dated Feb 7 2013 is identical to CLJ-1100-periods-in-data-reader-tags.patch dated Nov 29 2012, except it applies cleanly to latest master. The only change appears to be in some white space in the context lines.

I've removed clj-1100-periods-in-data-reader-tags-patch-v2.txt mentioned in the previous comment, because I learned that CLJ-1100-periods-in-data-reader-tags.patch dated Nov 29 2012 applies cleanly to latest master and passes all tests if you use this command to apply it.

Both of the current patches, CLJ-1100-periods-in-data-reader-tags.patch dated Nov 29 2012, and clj-1100-reader-literal-periods.patch dated Nov 6 2012, fail to apply cleanly to latest master (1.5.0-RC15) as of today, although they did last week. Given all of the changes around read / read-string and edn recently, they should probably be evaluated by their authors to see how they should be updated.

Andy Fingerhut
added a comment - 13/Feb/13 11:31 AM Both of the current patches, CLJ-1100-periods-in-data-reader-tags.patch dated Nov 29 2012, and clj-1100-reader-literal-periods.patch dated Nov 6 2012, fail to apply cleanly to latest master (1.5.0-RC15) as of today, although they did last week. Given all of the changes around read / read-string and edn recently, they should probably be evaluated by their authors to see how they should be updated.

Steve Miner
added a comment - 14/Feb/13 12:23 PM I deleted my patch: CLJ-1100-periods-in-data-reader-tags.patch. clj-1100-reader-literal-periods.patch is clearly wrong, but the original author or an administrator has to delete that.

Kevin, I'm not planning to work on this right now as 1.5 is pretty much done. It might be worthwhile discussing the issue a bit on the dev mailing list before working on a patch, but that's up to you. I think my approach was correct, although now changes would have to be applied to both LispReader and EdnReader.

Steve Miner
added a comment - 14/Feb/13 3:04 PM Kevin, I'm not planning to work on this right now as 1.5 is pretty much done. It might be worthwhile discussing the issue a bit on the dev mailing list before working on a patch, but that's up to you. I think my approach was correct, although now changes would have to be applied to both LispReader and EdnReader.

Steve Miner
added a comment - 28/Apr/14 8:21 AM Added patch to allow reader tags to have periods, but only with a namespace. Added tests to confirm that it works, but does not allow overriding a record name with a data-reader.

The patch implements Alex's alternative 1. It's purely lexical. A tag symbol without a namespace and containing periods is handled as a record (Java class). Otherwise, it's a data-reader tag. Of course, unqualified symbols without periods are still data-reader tags.

IMHO, a Java class without a package is a pathological case which Clojure doesn't need to worry about. This patch follows the convention that Java classes are named by unqualified symbols containing dots.

I did try alternative 2, testing for an actual class, but the implementation was more complicated. Also, it would open the possibility of breaking working code by adding a record or Java class that accidentally collided with an unqualified dotted tag that had previously worked fine. It's better to follow a simple rule that unqualified dotted symbols always refer to classes. Maybe the class doesn't actually exist, but that doesn't mean the symbol might be a data-literal tag.

Steve Miner
added a comment - 28/Apr/14 8:51 AM The patch implements Alex's alternative 1. It's purely lexical. A tag symbol without a namespace and containing periods is handled as a record (Java class). Otherwise, it's a data-reader tag. Of course, unqualified symbols without periods are still data-reader tags.
IMHO, a Java class without a package is a pathological case which Clojure doesn't need to worry about. This patch follows the convention that Java classes are named by unqualified symbols containing dots.
I did try alternative 2, testing for an actual class, but the implementation was more complicated. Also, it would open the possibility of breaking working code by adding a record or Java class that accidentally collided with an unqualified dotted tag that had previously worked fine. It's better to follow a simple rule that unqualified dotted symbols always refer to classes. Maybe the class doesn't actually exist, but that doesn't mean the symbol might be a data-literal tag.